Reactants:
* Water (H₂O): The source of electrons and protons (hydrogen ions).
* Light energy: This energy is absorbed by chlorophyll and other pigments within the chloroplasts.
Products:
* Oxygen (O₂): A byproduct of water splitting; it is released into the atmosphere.
* ATP (adenosine triphosphate): This is the energy currency of the cell.
* NADPH (nicotinamide adenine dinucleotide phosphate): An electron carrier that carries high-energy electrons to the light-independent reactions (Calvin cycle).
Summary of the Process:
1. Light Absorption: Light energy is captured by chlorophyll and other pigments in the chloroplasts.
2. Water Splitting: The energy from light is used to split water molecules, releasing oxygen gas as a byproduct.
3. Electron Transport Chain: Electrons from water are passed along a chain of electron carriers, releasing energy that is used to pump protons (H⁺) across the thylakoid membrane.
4. ATP Production: The proton gradient created across the thylakoid membrane drives ATP synthase, which produces ATP from ADP and inorganic phosphate.
5. NADPH Formation: The energized electrons from the electron transport chain are used to reduce NADP⁺ to NADPH.
Key Points:
* The light-dependent reactions take place within the thylakoid membranes of chloroplasts.
* This stage converts light energy into chemical energy in the form of ATP and NADPH, which are used in the light-independent reactions (Calvin cycle) to create sugar.
